This invention relates to the polymerization of cyclic olefins. In one embodiment, the invention relates to a catalyst for the reaction injection molding of dicyclopentadiene.
Cyclic olefins are subject to ring-opening metathesis polymerization to produce thermoset polymers having physical properties making them suitable for structural and electronic applications, such as molded car parts and electrical laminates. Such polymerizations are commonly carried out in reaction injection molding (RIM) processes, in which a metathesis catalyst and a monomer are charged to a heated mold, and polymerization of the monomer and forming of the polymer into the desired shape are carried out simultaneously in the mold.
In such RIM processes, it is important that the polymerization reaction occur rapidly and with as complete incorporation of the charged monomers as possible. It has been found in molding polydicyclopentadiene, for example, that the presence of unreacted monomers results in a molded part having a very unpleasant odor and less than optimum physical properties. In commercial RIM processes, it is economically desirable that the process be carried out in as short a cycle time as possible and at mold temperature at or near room temperature. It is also advantageous to be able to use an impure monomer stream and thus avoid extensive purification of the monomer prior to polymerization.
One metathesis catalyst system which has been successfully used in RIM processes is the combination of a phenol-treated transition metal salt, such as WOCl.sub.4 or WCl.sub.6, and a co-catalyst such as an aluminum or tin compound. In particular, a phenol-substituted tungsten combined with a tin hydride has been found highly efficient for monomer incorporation into the polymer. This catalyst also is highly active in a relatively impure dicyclopentadiene feed stream.
The use of the aluminum and tin co-catalysts, however, has certain drawbacks. Both co-catalysts require special handling because of toxicity concerns and sensitivity to air and moisture. In addition, tin co-catalysts are quite expensive. It would therefore be desirable to provide a co-catalyst for the polymerization of cyclic olefins which has low sensitivity to air and moisture and relatively low toxicity. It would also be desirable to replace the costly tin component of the catalyst without sacrificing catalyst activity.
It is therefore an object of this invention to provide a catalyst and process for the polymerization of cyclic olefins. In one embodiment, it is an object of the invention to provide a co-catalyst which has relatively low toxicity and is stable in the presence of air and moisture. In a further embodiment, it is an object of the invention to provide a reaction injection molding process.